explain ohms law in terms of resistance

The length and diameter of copper wire are found to be 100 and 0.002 m respectively consider that resistivity of the copper is 1.72 x 10'-8 ohm-m calculate the value of the resistance

Determine the current flowing through resistor R2. (assume Zener voltage is 3 volts and Diode forward voltage is 0.7V)

2. A bank of nickel-cadmium cells is used as the emergency lighting supply for a hospital. There are 100 cells connected in series and each has an A-hr rating of 120 A-hr. The bank has to be replaced, and the manufacturer is no longer supplying nickel-cadmium cells. It is decided to replace the cells with lead-acid cells. How many lead-acid cells will be required if each has an A-hr rating of 60 A-hr, and how should they be connected?